Cutting head for a cord type mower

ABSTRACT

A cutting head for a cord-type mower driven by an engine is disclosed. The cutting head includes a rotor capable of rotating about an axis and a bobbin with a cord wound on it. The bobbin can rotate relatively to the rotor about the axis in the rotor. The cutting head includes two types of cord feeding systems. The first cord feeding system automatically feeds a cord in response to cord wear. The second cord feeding system feeds a cord in response to a manual tapping operation executed during driving of the cutting head. The second cord feeding system disconnects one of the bobbin and rotor from the engine in response to the tapping operation.

This application is a continuation of application Ser. No. 07/998,420,filed Dec. 30, 1992, now U.S. Pat. No. 5,295,306 which is a division ofSer. No. 07/792,788, filed on Nov. 15, 1991 now U.S. Pat. No. 5,222,301.

This application claims the priority of Japanese Patent Application No.2-312500 filed on Nov. 16, 1990 which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a cutting head for a cordtype mower. More particularly, the present invention relates to a cordfeeding system for extending a cord wound on a bobbin in a rotary casingto a length necessary for mowing.

2. Description of the Related Art

Many conventional cord type mowers have systems in their cutting headsfor feeding new cord when the current cord length is insufficient. Also,manual-type cutting heads are known which permit manual extension of thecord wound on a bobbin.

At present, the so called tap-and-go type and automatic type cuttingheads are popular. For the tap-and-go type, the cord is feed therequired length by releasing an interlock between a bobbin and a rotarycasing. The interlock is released either by hitting or strongly pressingthe rotary casing against the ground. This type of cutting head isdisclosed in, for example, Japanese Utility Model Publication No.2-16595, Japanese Patent Publication No. 2-26922, U.S. Pat. No.4,161,820, U.S. Pat. No. 4,183,138, and U.S. Pat. No. 4,189,833.

For the automatic type, the interlock between the bobbin and rotarycasing is released by the centrifugal force which changes according tothe length of the cord that extends from the rotary casing. Thus, thedesired cord length can be maintained. This type of cutting head isdisclosed in, for example, Japanese Patent Publication No. 59-22484,Japanese Patent Laid-open No. 60-83508, Japanese Patent Laid-open No.63-79522, Japanese Patent Laid-open No. 2-163003, U.S. Pat. No.4,347,666, U.S. Pat. No. 4,607,431, U.S. Pat. No. 4,660,286, and U.S.Pat. No. 4,817,288.

For the tap-and-go type, it is necessary for the operator to frequentlycheck the length of the cord consumed during mowing and extend the cordby hitting the rotary casing against the ground at times or stronglypressing it. Otherwise, the mowing efficiency greatly decreases.Therefore, the operator always has to execute checking and hitting. Thechecking and hitting give a large mental burden and physical load to theoperator.

However, the tap-and-go type has the advantage that the operator canfreely set the cord length according to the state of the material (suchas grass) being cut. For example, when grass is soft, it is possible toimprove the operation efficiency by extending the cord length whichpermits to the cutter to mow at a faster rate. When grass is hard, it ispossible to insure that the grass is cut by setting the cord length to arelatively small value, which increases the cutting force of the cord.Therefore, some operators prefer the advantage of optionally setting thecord length according to the situation to the labor saving advantages ofthe automatic feeding devices.

Automatic type feed mechanism automatically extends the cord after ithas been worn to a predetermined length. Because the extending lengthdepends on the characteristics of the elastic body and heavy bob set inthe rotary casing, it is limited to a predetermined range. Therefore, tochange the extending length, the elastic body and heavy bob should bechanged. However, it is very troublesome to change the parts accordingto the type of operation. Therefore, the cord length is normally presetto an average length required during operation in a variety ofsituations.

Because the cord is automatically extended when the cord is worn due tomowing, the automatic-type cutting head does not require hitting by theoperator and is therefore easier to operate. However, because theoperator cannot optionally select the cord length, it is impossible toextend the cord longer than the set length or keep the cord shorter thanthe set length.

Thus, the tap-and-go type and the automatic type each have their ownfeatures. However, each of the features appears as both an advantage ordisadvantage. Because the tap-and-go type allows the operator tooptionally select the cord length, it easier for professional operatorsto use because it operates more efficiently.

The tap-and-go type, however, requires the operator to always payattention to the cord length and also requires that the rotary casing behit when the remaining cord becomes short. Therefore, during prolongedmowing, this type gives a larger burden and physical load to theoperator. Thus, the request (or demand) for the automatic type hasrecently been increasing in the professional market.

SUMMARY OF THE INVENTION

Accordingly, it is a primary objective of the present invention toprovide a compact automatic-type cutting head that can optionallyincorporate a tap-and-go function, which can compensate for thedisadvantages of the both types.

To achieve the foregoing and other objects and in accordance with thepurpose of the present invention, an improved cutting head for acord-type mower is provided. The cord-type mower has an engine fordriving the cutting head. The cutting head includes a rotor which canrotate about an axis and a bobbin on which a cord is wound. The bobbinis mounted in the rotor so that it can rotate relatively to the rotorabout the axis. A cord feed slot for leading the distal end of the cordfrom the bobbin to the outside of the rotor is formed on the peripheryof the rotor. Moreover, the cutting head has two types of cord feedingsystems.

The first cord feeding system automatically feeds the cord in responseto cord wear. The first cord feeding system is arranged to selectivelydisengage one of the bobbin and rotor from the engine to feed apredetermined length of the cord through the cord feed slot. Thedisengaged one of the bobbin and rotor slips relative to the other whenit is disengaged.

The second cord feeding system feeds the cord in response to a tappingoperation that is executed while the cutting head is being driven. Thesecond cord feeding system disconnects one of the bobbin and rotor fromthe engine in response to the tapping operation. Again, this causes thedisengaged one of the bobbin and rotor to slip relative to the other.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention that are believed to be novel areset forth with particularly in the appended claims. The invention,together with the objects and advantages thereof, may best be understoodby reference to the following description of the presently preferredembodiments together with the accompanying drawings in which:

FIGS. 1 through 13 show a first embodiment of the present invention;

FIG. 1 is a side view of a first embodiment of a cord-type mower inaccordance with the present invention;

FIG. 2 is a sectional view of a cutting head;

FIG. 3 is a partial sectional view of the cutting head showing aposition different from the cutting position in FIG. 2;

FIG. 4 is a sectional view of the cutting head of FIG. 2, taken alongthe line 4--4 of FIG. 2;

FIG. 5 is a sectional view of the cutting head of FIG. 2, taken alongthe line 5--5 of FIG. 2;

FIG. 6 is a sectional view of the cutting head of FIG. 2, taken alongthe line 6--6 of FIG. 2;

FIG. 7 is an exploded perspective view of the cutting head;

FIG. 8 is a perspective view of the control plate constituting thecutting head;

FIG. 9 is a perspective view of the bobbin constituting the cuttinghead;

FIG. 10 is a sectional view of the cutting head performing thetap-and-go operation;

FIG. 11 is a sectional view of the cutting head of FIG. 10, taken alongthe line 11--11 of FIG. 10;

FIG. 12 is a sectional view of the cutting head of FIG. 10, taken alongthe line 12--12 of FIG. 10;

FIG. 13 is a partially sectional view of a cutting head corresponding toFIG. 3, in which the cutting head serves as one dedicated to thetap-and-go operation using a stopper pin;

FIGS. 14 through 22 show a second embodiment of the present invention;

FIG. 14 is a sectional view of a cutting head corresponding to FIG. 2 ofthe first embodiment;

FIG. 15 is a partially sectional view of a cutting head corresponding toFIG. 3 of the first embodiment;

FIG. 16 is a sectional view of the cutting head of FIG. 14, taken alongthe line 16--16 of FIG. 14;

FIG. 17 is a sectional view of the cutting head of FIG. 14, taken alongthe line 17--17 of FIG. 14;

FIG. 18 is a sectional view of the cutting head of FIG. 14, taken alongthe line 18--18 of FIG. 14;

FIG. 19 is a sectional view of a cutting head corresponding to FIG. 10of the first embodiment;

FIG. 20 is a sectional view of the cutting head of FIG. 19, taken alongthe line 20--20 of FIG. 19;

FIG. 21 is a sectional view of the cutting head of FIG. 19, taken alongthe line 21--21 of FIG. 19;

FIG. 22 is a partially sectional view of a cutting head corresponding toFIG. 13 of the first embodiment;

FIGS. 23 through 30 show a third embodiment of the present invention;

FIG. 23 is a sectional view of a cutting head corresponding to FIG. 2 ofthe first embodiment;

FIG. 24 is a sectional view of the cutting head of FIG. 23, taken alongthe line 24--24 of FIG. 23;

FIG. 25 is a sectional view of the cutting head of FIG. 23, taken alongthe line 25--25 of FIG. 23;

FIG. 26 is a sectional view of a cutting head automatically feedingcords;

FIG. 27 is a sectional view of the cutting head of FIG. 26, taken alongthe line 27--27 of FIG. 26;

FIG. 28 is a sectional view of the cutting head of FIG. 26, taken alongthe line 28--28 of FIG. 26;

FIGS. 29 and 30 are sectional views of the cutting head serving as onededicated to the tap-and-go operation using a stopper pin;

FIGS. 31 through 39 show a fourth embodiment of the present invention;

FIG. 31 is a sectional view of a cutting head corresponding to FIG. 2 ofthe first embodiment;

FIG. 32 is a partially sectional view of a cutting head corresponding toFIG. 3 of the first embodiment;

FIG. 33 is a sectional view of the cutting head of FIG. 31, taken alongthe line 33--33 of FIG. 31;

FIG. 34 is a sectional view of the cutting head of FIG. 31, taken alongthe line 34--34 of FIG. 31;

FIG. 35 is a sectional view of the cutting head of FIG. 31, taken alongthe line 35--35 of FIG. 31;

FIG. 36 is a sectional view of a cutting head corresponding to FIG. 10of the first embodiment;

FIG. 37 is a sectional view of the cutting head of FIG. 36, taken alongthe line 37--37 of FIG. 36;

FIG. 38 is a sectional view of the cutting head of FIG. 36, taken alongthe line 38--38 of FIG. 36;

FIG. 39 is a partially sectional view of a cutting head corresponding toFIG. 13 of the first embodiment;

FIGS. 40 through 49 show a fifth embodiment of the present invention;

FIG. 40 is a sectional view of a cutting head corresponding to FIG. 2 ofthe first embodiment;

FIG. 41 is a partially sectional view of a cutting head corresponding toFIG. 3 of the first embodiment;

FIG. 42 is a sectional view of the cutting head of FIG. 40, taken alongthe line 42--42 of FIG. 40;

FIG. 43 is a sectional view of the cutting head of FIG. 40, taken alongthe line 43--43 of FIG. 40;

FIG. 44 is a sectional view of the cutting head of FIG. 40, taken alongthe line 44--44 of FIG. 40;

FIG. 45 is a sectional view of a cutting head corresponding to FIG. 10of the first embodiment;

FIG. 46 is a sectional view of the cutting head of FIG. 40, in whichdrive rinks are moved from the state in FIG. 42 due to the centrifugalforce;

FIG. 47 is a sectional view of the cutting head of FIG. 45, taken alongthe line 47--47 of FIG. 45;

FIG. 48 is a sectional view of the cutting head of FIG. 45, taken alongthe line 48--48 of FIG. 45;

FIG. 49 is a partially sectional view of a cutting head corresponding toFIG. 13 of the first embodiment;

FIGS. 50 through 58 show a sixth embodiment of the present invention;

FIG. 50 is a sectional view of a cutting head corresponding to FIG. 2 ofthe first embodiment;

FIG. 51 is a partially sectional view of a cutting head corresponding toFIG. 3 of the first embodiment;

FIG. 52 is a sectional view of the cutting head of FIG. 50, taken alongthe line 52--52 of FIG. 50;

FIG. 53 is a sectional view of the cutting head of FIG. 50, taken alongthe line 53--53 of FIG. 50;

FIG. 54 is a sectional view of the cutting head of FIG. 50, taken alongthe line 54--54 of FIG. 50;

FIG. 55 is a sectional view of a cutting head corresponding to FIG. 10of the first embodiment;

FIG. 56 is a sectional view of the cutting head of FIG. 55, taken alongthe line 56--56 of FIG. 55;

FIG. 57 is a sectional view of the cutting head of FIG. 55, taken alongthe line 57--57 of FIG. 55;

FIG. 58 is a partially sectional view of a cutting head corresponding toFIG. 13 of the first embodiment;

FIGS. 59 through 66 show the seventh embodiment of the presentinvention;

FIG. 59 is a sectional view of a cutting head corresponding to FIG. 2 ofthe first embodiment;

FIG. 60 is a partially sectional view of the cutting head in FIG. 59,viewed in a position 45° displaced from the sectional position in FIG.59;

FIG. 61 is a sectional view of the cutting head of FIG. 59, taken alongthe line 61--61 of FIG. 59;

FIG. 62 is a sectional view of the cutting head of FIG. 59, taken alongthe line 62--62 of FIG. 59;

FIG. 63 is a sectional view of the cutting head of FIG. 59, taken alongthe line 63--63 of FIG. 59;

FIG. 64 is a sectional view of a cutting head automatically feedingcords;

FIG. 65 is a sectional view of a cutting head during tapping;

FIG. 66 is a sectional view of the cutting head of FIGS. 64 and 65,taken along the line 66--66 of FIGS. 64 and 65;

FIGS. 67 through 72 show the eighth embodiment of the present invention;

FIG. 67 is a partially sectional view of a cutting head;

FIGS. 68 and 69 show a cutting head viewed from the bottom of it withouta cover constituting the casing of the cutting head;

FIG. 70 is a partially sectional view of a cutting head during tapping;

FIG. 71 is a partially sectional view of a cutting head serving as onededicated to the tap-and-go operation using a stopper pin; and

FIG. 72 is a partial view of the cutting head in FIG. 71 viewed from thebottom of it.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The first through eighth embodiments of the present invention will bedescribed below with reference to the accompanying drawings.

First embodiment

The first embodiment of the present invention is described belowaccording to FIGS. 1 through 13. As shown in FIG. 1, the cord type mowerhas a cutting head 1, an engine 3, and a shaft tube 2. The shaft tube 2connects the head 1 with the engine 3 and transmits the power of theengine 3 to the head 1. The head 1 is operated by the engine 3 throughthe tube 2. The following is the detailed description of the head 1.

As shown in FIG. 2, a rotary casing 4 of the head 1 has a housing 5 anda protective cover 6. The casing 4 is connected to a drive shaft (notillustrated) rotatably installed in the tube 2 by a center bolt 7 at thecenter of the housing 5. Therefore, the housing 5 and the cover 6 arerotated together around an axis 7a of the center bolt 7.

A bobbin 8 and a control plate 9 coupled to the bobbin 8 are stored inthe casing 4 so that they can rotate around the axis 7a independently ofthe casing 4. A pair of cord feed slots 10 are provided on the outerperiphery of the housing 5 and are spaced apart by an interval of 180°.

The bobbin 8 has upper and lower section and one of two cords 11 iswound about each bobbin section. The end of each cord 11 passes throughan associated one of the slots 10 and extends outside the housing 5.

As shown in FIGS. 2 and 7, four drive links 12 are installed in thehousing 5 such that they are positioned around the axis 7a at 90°intervals. Each link 12 can move in the radial direction of the housing5 within the housing.

As shown in FIG. 4, a groove is provided in the top surface of the plate9. The groove is composed of eight radial groove sections 13 and eightguide groove sections 14 that connect the radial grooves 13. The radialgrooves 13 extend generally in the radial direction of the plate 9 andare provided at equal angular intervals about the center bolt 7.Adjacent radial and guide grooves 13 and 14 cooperate to form an innerstep 13a nearer to the center bolt 7 and an outer step 13b farther fromthe center bolt 7.

A link stud 12a protrudes from the lower surface of each link 12. Theselink studs 12a extend into the plate groove. Thus, they are typicallypositioned in four of the radial groove sections 13. That is, in everyother radial groove. Each link 12 is biased in the direction of the axis7a by a compression coil spring 15 such that the link stud 12a isnormally pressed against the step 13a of the groove 13 by the pressureof the spring 15. When the casing 4 is rotated under the above state,the plate 9 is rotated together with the casing 4 in the same directiondue to the engagement with each link 12.

When the links 12 move radially outward against the pressure of thespring 15, the stud 12a of each link 12 moves from a position thatengages the step 13a (i.e. stop position) toward the step 13b. When thestud 12a is released from the step 13a, the plate 9 relatively rotatesin the direction opposite to the rotational direction of the casing 4and the stud 12a moves to the linking position of the next radial groove13 by following the guide groove 14.

As shown in FIG. 7, eight projections 16 are provided on the top surfaceof the bobbin 8 at equally spaced intervals. Each projection includes atapered surface 16a which tilts in the same direction as the projection.As shown in FIG. 9, eight projections 17 are provided on the bottomsurface of the bobbin 8 at equally spaced intervals. The projections 17thus each include a tapered surface 17a. Each projection 16 at the topand each projection 17 at the bottom are installed corresponding to thesame angular position in a concentric circle. The surfaces 16a and 17atilt in the opposite direction to each other.

As shown in FIG. 8, eight tapered recesses 18 are formed on the bottomsurface of the plate 9 at equally spaced intervals. The recesses 18 eachinclude a tapered surface 18a. As shown in FIGS. 2 and 7, eight taperedrecesses 19 are also formed on the inside bottom surface of the cover 6at an equally spaced intervals. The recesses 19 also each include atapered surface 19a.

As shown in FIGS. 5 and 6, each tapered recess 18 of the plate 9 andeach recess 19 of the cover 6 are arranged along the periphery so thatthe former are staggered from the latter by 2.sub.π /16 radians. Inaddition, the tapered surface 18 and the surface 19a tilt in theopposite directions.

The bobbin 8 can slide along the axis 7a in the casing 4 and is pressedupward by a compression coil spring 20 supported by the cover 6. Asshown in FIGS. 2, 5, and 6, the pressure of the spring 20, pushes theprojections 16 into the recesses 18 of the plate 9. At the same time,the projections 17 on the bottom surface of the bobbin 8 are separatedfrom the recesses 19 of the cover 6.

As shown in FIGS. 10, 11, and 12, when the bobbin 8 moves downwardagainst the biasing force of the spring 20, the projections 16 on thetop surface of the bobbin 8 separate from the recesses 18. At the sametime, the projections 17 engage the recesses 19 in the cover 6.

As shown in FIG. 7, a pair of bores 22 are formed in the upper surfaceof housing 5 at positions separated by an interval of 180°. A pair ofholes 23 are formed on the plate 9 such that they are aligned with thebores 22.

As shown in FIG. 3, when a short pin 24 is inserted into the bore 22 ofthe housing 5, the plate 9 can rotate independently of the housing 5. Asshown in FIG. 13, however, when a long stopper pin 25 is inserted intothe bore 22 of the housing 5 it extends into the hole 23 of the plate 9.Thus, the housing 5 always rotates together with the plate 9.

As shown in FIG. 3, when the short pin 24 is used, the head 1 has theautomatic and tap-and-go feeding functions. In this configuration, whenthe casing 4 is rotated in the state shown in FIGS. 2 and 4, the plate 9is rotated therewith due to its engagement with the link stud 12a.Moreover, the bobbin 8 is also rotated due to the fact that the topprojections 16 engage the recesses 18 in plate 9. In this case, the cord11 which extends through the slot 10 is also rotated to cut grass or thelike.

When the cord 11 is consumed during mowing, the rotating resistance ofthe casing 4 decreases. Thus, the rotational speed of the casing 4increases when compared to the speed attained when a normal length ofthe cord 11 extends from the casing (given a constant engine output).Therefore, the centrifugal force acting on the links 12 increasescausing the links 12 to move radially outward against the pressure ofthe spring 15. Accordingly, the studs 12a move from the stop position intheir corresponding radial grooves 13 to the release position.

In the release position, the stud 12a slides along the groove 14 due tothe rotation of the casing 4. Specifically, since the rotation of thecasing 4 is not transmitted to the plate 9. The bobbin 8 slips relativeto the casing 4. Accordingly, the bobbin 8 rotates relatively to thecasing 4.

The cord 11 is wound in a direction that is opposite to the rotationaldirection of the casing 4. When the plate 9 and the bobbin 8 sliprelative to the casing 4, the slot 10 rotates together with the casing4. Therefore, the distal end of the cord 11 follows the rotation of thecasing 4. Thus, the cord 11 is feed into the internal space of thecasing 4 a distance equivalent to the distance the bobbin 8 slipsrelative to the casing 4. Centrifugal force then draws the feed cord 11outside of the casing through the slot 10.

As the cord 11 is feed, the rotational resistance of the casing 4gradually increases which reduces the speed of the casing 4. As thespeed of the casing 4 decreases, the centrifugal force working on thelink 12 decreases and the link 12 returns toward the axis 7a by theforce of the spring 15. Thus, the stud 12a of the link 12 reaches thestop position of the adjacent groove 13. As a result, the casing 4 hasbeen rotated a distance of 2.sub.π /8 radians (45°) relative to thebobbin 8. Then, the plate 9 and the bobbin 8 rotate together with thecasing 4 until the cord 11 is again worn due to use.

In this type of automatic system, after a predetermined length of thecord 11 has been worn, the extending operation is repeated and the cord11 is automatically extended. It is possible to control the distancethat the cord 11 extends beyond the slot after a feeding operation byadjusting the force provided by spring 15. That is, when the springtension is set relatively high, the automatic feeding operation will notbe executed until the length of cord extending from slot 10 isrelatively short. Thus, the length of the cord after the feedingoperation has been completed will be relatively shorter.

When the head 1 is used in the automatic mode, the length of the cord 11to be feed from the slot 10 is normally set to a constant value in thistype of automatic feeding. On the other hand, when the head is used inthe tap-and-go mode, it is possible to extend the cord 11 a totaldistance that is longer than the above set value.

In the tap-and-go mode, the cord is feed by hitting the casing 4 againstthe ground. More specifically in the state shown in FIGS. 2, 5, and 6,the casing is hit against the ground while it rotates. The impact drivesthe bobbin 8 against the pressure of the spring 20 as shown in FIGS. 10,11, and 12. The bottom projections 17 of the bobbin 8 thus contact therecesses 19 in the cover 6 in an offset manner. Thus, a part of thetapered surface 17a of the projection 17 contacts a part of the taperedsurface 19a of the recess 19. The casing 4 and the plate 9 then rotaterelative to the bobbin 8 by the amount the bottom projections 17 areoffset from the recesses 19. That is 2.sub.π /16 radians. At this point,the bobbin 8 again rotates together with the casing 4 and the plate 9.While the bobbin 8 slips relative to the casing 4, the cord 11 is feed acorresponding amount.

Since the spring 20 is compressed by the downward moving bobbin 8 due tothe inertia created by the hitting actions, the bobbin 8 is thereafterpushed upward by the action of the spring 20. The top projection 16 ofthe bobbin 8 is thus inserted into the recess 18 of the plate 9 and apart of the surface 16a of the projection 16 contacts a part of thesurface 18a of the recess 18.

Then, similarly to the above mentioned, the casing 4 and the plate 9rotate 2.sub.π /16 radians relative to the bobbin 8 which feeds the cord11 accordingly. When the surface 16a completely fits with the surface18a, the bobbin 8 again rotates together with the casing 4 and the plate9. By using the described tap-and-go function, the cord 11 is extendedfrom the bobbin 8 by the length corresponding to 4.sub.π /16 radianseach time the casing is tapped.

The head 1 having both the automatic and tap-and-go systems makes itpossible to set the length of the cord 11 longer than the extendinglength set by the automatic system by hitting the casing 4 against theground as desired.

In another mode shown in FIG. 13, pins 25 are inserted into the housingbores 22 and the plate holes 23, the plate 9 does not rotate relativelyto the casing 4 and the cord 11 is not automatically extended.Therefore, it is possible to operate only the tap-and-go systemindependently of the automatic system. In this case, the length of thecord 11 to be extended is determined according to the number of timesthe case is tapped.

As described above, because the head 1 of the first embodiment has boththe automatic and tap-and-go systems, the operator can use both oreither one of the two systems according to the situation. Therefore, thedisadvantages of the conventional cutting heads having only one of theautomatic and tap-and-go system are eliminated. Moreover, thisembodiment makes the head compact by arranging both of the systems alongthe axis 7a.

Second embodiment

The second embodiment of the present invention is described below withreference to FIGS. 14 through 22. It is noted that in many respects thedesign is similar to the design described above with reference to thefirst embodiment. Therefore, the discussion below primarily stresses thedifferences from the first embodiment.

The second embodiment is different from the first embodiment in theconstruction of a drive link 12 and its urging system. That is, for thesecond embodiment, just two links 12 are provided. As seen in FIGS. 14and 16, the links are located 180° apart from each other relative to thehousing axis 7a. Each link 12 is rotatably supported on the housing 5 bya pivot pin 26.

A link stud 12a protrudes from the bottom end of each link 12. The stud12a, similarly to the procedure in the first embodiment, is insertedinto a radial groove 13 of a control plate 9. A rotary sleeve 27 ispositioned at the center in the housing 5. A torsion coil spring 71 forrotatably urging the sleeve 27 in FIG. 16 is journaled about the sleeve27.

As shown in FIG. 16, gear type teeth on the link 12 engage similar teethon the outer periphery of the sleeve 27. Therefore, the studs 12a of thelinks 12 are urged by the spring 71 such that they press against anassociated inner step 13a.

Other portions of the second embodiment are basically the same as thoseof the first embodiment. Therefore, a portion corresponding to that ofthe first embodiment is provided with the same number as the firstembodiment. FIGS. 14, 15, 16, 17, 18, 19, 20, 21, and 22 of the secondembodiment correspond to FIGS. 2, 3, 4, 5, 6, 10, 11, 12, and 13 of thefirst embodiment respectively.

This construction rotates each link 12 against the action of the spring71 through the sleeve 27 so that the stud 12a moves outward when thecentrifugal force acting on each link 12 increases as the speed of arotary casing 4 increases. Thus, the stud 12a moves from the stopposition to the release position within the radial groove 13.

When cords 11 are extended up to a certain length similarly to procedurein the first embodiment, the speed of the casing 4 decreases and thecentrifugal force acting on the link 12 decreases. Therefore, the links12 are returned by the action of the spring 71. Thus, the automaticfeeding of the cords 11 is controlled.

Third embodiment

The third embodiment of the present invention is described withreference to FIGS. 23 through 30. Again the differences from the firstembodiment are stressed in the following description.

As shown in FIG. 23, the third embodiment does not have the controlplate 9 used for the first embodiment. Rather a bobbin 8 is located inthe casing 4 so that it can rotate relative to the casing 4 around anaxis 7a. Because the plate 9 of the first embodiment is not used, theconstruction of a drive link 12 is also different from that of the firstembodiment.

That is, an aperture 28 is formed at the center of the bobbin 8 and theinternal surface of the aperture 28 serves as a surface 28a. The surface28a gradually tilts outward from the axis 7a. A center pin 29 ispositioned at the center of the bobbin so that it can be verticallymoved. A support plate 30 is mounted to the center pin 29 above theaperture 28.

As shown in FIG. 24, four drive links 72 are located between the plate30 and aperture 28 at 90° intervals so that they surround the center pin29. The bottom surface 72b of each link 72 extends diagonally. Thesurface 72b of each link 72 contacts the surface 28a of the aperture 28.Each link 72 is mutually connected by an extension coil spring 73 sothat it approaches the center pin 29.

As shown in FIGS. 23 and 24, eight teeth 31 are mounted on the topsurface of the bobbin 8 at equally spaced intervals. Also, as shown inFIGS. 23 and 25, eight teeth 32 are mounted on the bottom surface of thebobbin 8 at equally spaced intervals. Each top tooth 31 is displacedfrom each bottom tooth 32 by 2.sub.π /16 radians under the state shownin FIGS. 24 and 25.

Eight teeth 33 are located inside the housing 5 at equally spacedintervals and eight teeth 34 are located on a protective cover 6 atequally spaced intervals. Each tooth 33 of the housing 5 and each tooth34 of the cover 6 are located at the same angular position.

The bobbin 8 is slidably mounted along the axis 7a and is urged upwardby a compression coil spring 20 supported on the cover 6. As shown inFIGS. 23, 24, and 25, the teeth 32 under the bobbin 8 are verticallyseparated from the teeth 34 of the cover 6 by the action of the spring20. The spring also urges the teeth 31 above the bobbin 8 to engage withthe teeth 33 of the housing 5.

As shown in FIGS. 26, 27, and 28, centrifugal force will urge the links72 outward from the axis 7a against the action of the spring 73 when thecasing 4 rotates. Outward movement of the links presses the bobbin 8downward. That is the bobbin's aperture surface 28a is pressed downwardby the link surfaces 72b. As a result, the bobbin 8 moves downward. Whenthis occurs, the top teeth 31 of the bobbin 8 separates from the teeth33 of the housing 5 and the bottom teeth 32 of the bobbin 8 engage theteeth 34 of the cover 6.

As shown in FIG. 23, four bores 36 are formed on the housing 5 at theintervals of 90°. Four bores 37 are also formed on a support plate 30 atpositions corresponding to the bores 36 of the housing 5. Therefore, asshown in FIGS. 23 and 26, when short pins 38 are inserted into the bores36 of the housing 5, the links 72 are able to move in the radialdirection independently of the short pins 38. However, as shown in FIGS.29 and 30, when stopper pins 39 are inserted into the bores 36 and 37,the bottom end of the stopper pins 39 enter the aperture 28. Therefore,the stopper pins 39 prevent the links 72 from moving radially outward.

As shown in FIG. 23, when the short pins 38 are inserted into only thebores 36 of the housing 5, a cutting head 1 has both the automatic andtap-and-go functions. When the casing 4 under the state shown in FIGS.23, 24, and 25 rotates, the bobbin 8 also rotates because the teeth 33of the housing 5 are engaged with the top teeth 31 of the bobbin 8. Inthis case, a cord 11 extended from a cord feed slot 10 of the casing 4also rotates to execute mowing.

When the cords 11 are consumed due to mowing, the speed of the casing 4increases as described in the first embodiment. Thus, the centrifugalforce acting on each link 72 increases and the links 72 move radiallyoutward against the spring 73. Thus, the bobbin 8 is pressed downward atsurfaces 28a by the links 72.

In this case, as shown in FIGS. 26, 27, and 28, the bobbin 8 movesdownward against the action of the spring 20 and rotation of the casing4 is not transmitted to the bobbin 8 because the top teeth 31 of thebobbin 8 separate from the teeth 33 of the housing 5. Thus, the bobbin 8slips relative to the casing 4, and the cord 11 is extended outward fromthe slot 10 by the length corresponding to the difference of rotationalangle between the casing 4 and the bobbin 8, similarly to the firstembodiment.

When the casing 4 slips by approximately 2.sub.π /16 radians relativelyto the bobbin 8, the bottom teeth 32 of the bobbin 8 are engaged withthe teeth 34 of the cover 6 and the bobbin 8 rotates again by followingthe casing 4. However, when the rotational resistance of the casing 4increases after the cord 11 is extended, the speed of the casing 4decreases. Accordingly, the centrifugal force acting on each link 72also decreases and the links 72 are returned toward the axis 7a by theaction of the spring 73. Accordingly, the bobbin 8 is raised by theaction of the spring 20 and the bottom teeth 32 of the bobbin 8 separatefrom the teeth 34 of the cover 6. As a result, rotation of the casing 4is not transmitted to the bobbin 8.

Then, the bobbin 8 slips relative to the casing 4, while, as describedabove, the cords 11 are extended outward by the length corresponding tothe difference of rotational angle between the casing 4 and the bobbin8. When the casing 4 slips by approximately 2.sub.π /16 radiansrelatively to the bobbin 8, the top teeth 31 of the bobbin 8 engage withthe teeth 33 of the housing 5 and the bobbin 8 rotates again togetherwith the casing 4.

In accordance with this embodiment, when the cords 11 wears off by acertain length, they are automatically fed by a length corresponding to4.sub.π /16 radians each time the bobbin 8 vertically reciprocates.

The following is the description for use of the tap-and-go system. Whenthe casing 4 under the state shown in FIGS. 23, 24, and 25 is hitagainst the ground, the bobbin 8 is moved downward by the hitting impactagainst the spring 20 as shown in FIG. 26. Thus, the cords 11 are fedsimilarly to the procedure in the automatic system. The spring 20 iscompressed as the bobbin 8 is lowered due to the hitting operation. Whenthe inertia of the bobbin is absorbed, the bobbin 8 is pushed upward dueto the action of the spring 20 and the cords 11 are fed similarly to theprocedure in the automatic system.

Thus, the head 1 of this embodiment makes it possible to set the lengthof the cord 11 longer than the extending length set by the automaticsystem by hitting the casing 4 against the ground as desired.

In another mode shown in FIGS. 29 and 30, the stopper pins 39 areinserted into the housing 5. In this mode, the links 12 cannot move andthe cords 11 can not be automatically extended. Therefore, in this case,only the tap-and-go system operates similarly to the procedure in thefirst embodiment.

Fourth embodiment

The fourth embodiment of the present invention is described below withreference to FIGS. 31 through 39. Again the differences from the firstembodiment are stressed.

In the first embodiment, the bobbin 8 and the plate 9 are rotatablysupported independently of the casing 4. In contrast, in the fourthembodiment, the bobbin 8 always rotates together with a protective cover6 as shown in FIG. 31.

A shifter 40 is set between the bobbin 8 and a control plate 9. Theshifter 40 rotates relatively to a rotary casing 4. A pair of cord feedslots 10 are provided on the outer periphery of the shifter 40 and arespaced apart by an interval of 180°. The end of a cord 11 passes throughthe slots 10 and extends beyond a housing 5.

As shown in FIGS. 31 and 34, eight projections 41 are provided on thetop surface of the shifter 40 along the periphery at equally spacedintervals. As shown in FIGS. 31 and 35, eight projections 42 provided onthe bottom surface of the shifter 40 along its periphery at equallyspaced intervals. Each top projection 41 and each bottom projection 42are located at the same angular position.

Eight recesses 43 are provided on the bottom surface of the plate 9 atequally spaced intervals. Eight recesses 44 are provided on the uppersurface of the cover 6 at equally spaced intervals. In the state shownin FIGS. 34 and 35, each recess 43 of the plate 9 is displaced from eachrecess 44 of the cover 6 by 2.sub.π /16 radians in the circumferentialdirection.

The bobbin 8 and the shifter 40 are slidable along an axis 7a and urgedupward by a compression coil spring 20 supported by the cover 6.

As shown in FIGS. 31, 34, and 35, the top projections 41 of the shifter40 are received by the recesses 43 of the plate 9 and the bottomprojections 42 of the shifter 40 are separated the correspondingrecesses 44 of the cover 6 by the action of the spring 20 respectively.FIGS. 36, 37, and 38 show the state in which the bobbin 8 and theshifter 40 move downward against the action of the spring 20. In thiscase, the bottom projections 42 are received by the cover recesses 44and the top projections 41 are spaced from the plate recesses 43.

As shown in FIG. 32, when a short pin 24 is inserted into only a bore 22of the housing 5, a cutting head 1 has both the automatic and tap-and-gofunctions. In this case, the casing 4 under the state shown in FIGS. 31and 33 rotates together with the bobbin 8. The plate 9 is rotated due toengagement with link studs 12a of drive links 12. Moreover, the shifter40 is rotated due to engagement between the plate recesses 43 and thetop projections 41 of the shifter 40. In this case, the cords 11 alsorotates to cut grass.

When the cords 11 are worn off due to mowing, the speed of the casing 4increases and the centrifugal force acting on the links 12 increases,similarly to the situation described in the first embodiment.Accordingly, the links 12 separate from the axis 7a against acompression coil spring 15 and the projection 12a of each link 12 movesfrom a stop position to a release position in their radial groove 13 ofthe plate 9.

In the above state, the rotation of the casing 4 is not transmitted tothe plate 9. Therefore, the shifter 40 slips relative to the casing 40as the casing 4 rotates. Because the bobbin 8 rotates together with thecasing 4, the cords 11 extend beyond the casing 4 by the lengthcorresponding to the difference of rotational angle between the shifter40 and the casing 4 (or bobbin 8).

When the bobbin 8 slips by approximately 2.sub.π /8 radians relative tothe shifter 40 and the cords 11 are extended, the speed of the casing 4decreases in a manner similar to the situation described in the firstembodiment. Accordingly, the centrifugal force acting on the link 12decreases and the link 12 returns toward the axis 7a due to the actionof the spring 15. Thus, each projection 12a reaches a stop position ofthe adjacent slide groove 13, and the plate 9 and the shifter 40 rotateagain together with the casing 4 and the bobbin 8.

As described above, the head 1 of this embodiment is similar to thatdescribed in the first embodiment in that it automatically feeds thecords 11 by a predetermined length when they are worn to a predeterminedlength.

The following is the description of the use of the tap-and-go system.When the casing 4 in the state shown in FIGS. 31, 34, and 35 is hitagainst the ground, the bobbin 8 and the shifter 40 move downwardagainst the action of the spring 20. Then, the bottom projections 42 ofthe shifter 40 are inserted into the recesses 44 of the cover 6.

When the casing 4, bobbin 8, and plate 9 rotate by approximately 2.sub.π/16 radians relative to the shifter 40, the bottom projections 42 of theshifter 40 engage the recesses 44 of the cover 6. Then, the shifter 40rotates again together with the casing 4, bobbin 8, and plate 9.Therefore, the cords 11 are fed by the length corresponding to thedifference of rotational angle between the shifter 40 and the casing 4.

Once the downward inertia of the bobbin 8 and the shifter 40 has beenovercome by the compression of spring 20 the bobbin 8 and the shifter 40are moved upward by the action of the spring 20. As the shifter 40 movesupward, the top projections 41 of the shifter 40 are inserted into therecesses 43 of the plate 9.

When the casing 4, bobbin 8, and plate 9 slip by approximately 2.sub.π/16 radians relative to the shifter 40, the cords 11 are extended by thelength corresponding to the difference of rotational angle between theshifter 40 and the casing 4 as mentioned above. When the top shifterprojections 41 engage with the plate recesses 43, the shifter 40 rotatesagain together with the casing 4 and the plate 9. Thus, the fourthembodiment allows the operator to set the length of the cord 11 longerthan the extending length set by the automatic system by hitting thecasing 4 against the ground as desired.

In the mode shown in FIG. 39, when stopper pins 25 are inserted into thebores 22 of the housing 5 and the bores 23 of the plate 9, automaticfeed of the cord 11 is prohibited and only the tap-and-go systemoperates, similarly to the situation described in the first embodiment.

Fifth embodiment

The fifth embodiment of the present invention is described below withreference to FIGS. 40 through 49. Again the differences from the firstembodiment are stressed.

For the fifth embodiment, a housing 5 and a protective cover 6 whichconstitute a rotary casing 4 are assembled inversely to those of thefirst embodiment as shown in FIG. 40. Therefore, a shaft tube 2 ismounted on the cover 6. Accordingly, the positions of a bobbin 8, acontrol plate 9, and each drive link 12 are changed.

As shown in FIGS. 41 and 42, eight teeth 46 are provided on the bottomsurface of the plate 9 at equally spaced intervals. Eight teeth 47 arealso provided on the bottom surface of the plate 9 at equally spacedintervals. The teeth 46 and the teeth 47 are displaced from each otherby 2.sub.π /16 radians.

Each drive link 12 is urged toward an axis 7a by a compression coilspring 15 and the link stud 12a of each link 12 is ready to engage withthe inside teeth 46 of the plate 9. When the casing 4 rotates, the plate9 also rotates in the same direction as the casing 4 due to engagementbetween the studs 12a and the inside teeth 46 of the plate 9.

As shown in FIG. 46, when the links 12 move radially outward from theaxis 7a against the action of the spring 15, the studs 12a separate fromthe inside teeth 46 of the plate 9 and such that then can engage theoutside teeth 47 of the plate 9.

As shown in FIGS. 40 and 43, eight teeth 48 are provided on the bottomsurface of a bobbin 8 at equally spaced intervals. As shown in FIGS. 40and 44, eight teeth 49 are provided on the top surface of the bobbin 8at equally spaced intervals. The bottom teeth 48 and the top teeth 49are located at the same angular positions.

Eight recesses 50 are formed on the top surface of the plate 9 atequally spaced intervals. Eight holes 51 are formed on the top wall ofthe cover 6 at equally spaced intervals. Under the state shown in FIGS.43 and 44, the recesses 50 of the plate 9 and the holes 51 of the cover6 are displaced by 2.sub.π /16 radians.

As shown in FIG. 40, a center boss 52 is mounted at the center of thebottom surface of the bobbin 8, which is exposed to the outside throughthe center of the housing 5. The bobbin 8 and the boss 52 are supportedso that they can move along the axis 7a and are urged downward by thespring 20. By the action of the spring 20, the top teeth 49 of thebobbin 8 separate from the cover holes 51 and the bottom teeth 48 of thebobbin 8 are inserted into the plate recesses 50.

As shown in FIGS. 45, 47 and 48, when the bobbin 8 and the boss 52 aremoved upward against the action of the spring 20, the bottom teeth ofthe bobbin 8 separate from the recesses 50 of the plate 9 and the topteeth of the bobbin 8 are inserted into the holes 51 of the cover 6.

As shown in FIG. 41, when short pins 24 are inserted into the bores 22of the housing 5, the cutting head 1 has both automatic and tap-and-gofunctions. In this case, when the casing 4 under the state shown inFIGS. 40 and 42 rotates, the plate 9 is rotated due to engagementbetween the link studs 12a and the inside teeth 46 of the plate 9.Moreover, the bobbin 8 is rotated due to engagement between the platerecesses 50 and the bottom teeth 48 of the bobbin 8. The cords 11 rotatetogether with the casing 4 and the bobbin 8.

When the cords 11 are worn due to mowing, the centrifugal force actingon each link 12 increases similarly to the situation described in thefirst embodiment. Then, the links 12 separate from the axis 7a againstthe spring 15 and the link stud 12a separates from the inside teeth 46of the plate 9 to enter the rotational route of the outside teeth 47.

When the link studs 12a are not engaged with the inside teeth 46 of theplate 9, rotation of the casing 4 is not transmitted to the plate 9.Therefore, the bobbin 8 and the boss 52 slip relative to the casing 4.Then, the cords 11 are extended outward due to the centrifugal forcewhile the difference of rotational speed occurs between the plate 9,bobbin 8, and boss 52 on one hand and the casing 4 on the other.

When the casing 4 slips by approximately 2.sub.π /16 radians relativelyto the bobbin 8, the link stud 12a engage the outside teeth 47 of theplate 9. Thus, the plate 9, bobbin 8, and boss 52 rotate again togetherwith the casing 4.

When the cords 11 are fed by a designated length, the speed of thecasing 4 decreases and the centrifugal force acting on each link 12 alsodecreases. Then, each link 12 is moved toward the axis 7a by the actionof the spring 15. As a result, the stud 12a of each link 12 separatesfrom the outside teeth 47 of the plate 9 and enters the rotational routeof the inside teeth 46 of the plate 9.

As above mentioned, when the link studs 12a are not engaged with theoutside teeth 47 of the plate 9, rotation of the casing 4 is nottransmitted to the plate 9. Therefore, the bobbin 8 and the boss 52slip. Thus, while the difference of rotational speed occurs between theplate 9, bobbin 8, and boss 52 on one hand and the casing 4 on theother, the cords 11 are extended outward by the centrifugal force.

When the casing 4 slips by approximately 2.sub.π /16 radians relativelyto the bobbin 8, the link studs 12a engage with the inside teeth 46 ofthe bobbin 8, and the plate 9. At that point, bobbin 8 and boss 52rotate together with the casing 4. Therefore, this embodimentautomatically feeds the cords 11 of a certain length by repeating theoperation previously mentioned when the cords 11 wear off by a certainlength.

The following is the description for use of the tap-and-go system. Whenthe boss 52 of the head 1 under the state in FIGS. 40, 43, and 44 is hitagainst the ground, the boss 52 moves upward together with the bobbin 8against the action of the spring 20. Then the top bobbin teeth 49 areinserted into the cover holes 51 as shown in FIGS. 45, 47, and 48. Atthis point casing 4 slips relative to the bobbin 8 and boss 52 byapproximately 2.sub.π /16 radians. Accordingly, the top bobbin teeth 49engage the cover holes 51, and the bobbin 8 and boss 52 rotate togetherwith the casing 4. Thus, like in the automatic function, the cords 11are fed while the difference of rotational speed occurs between thebobbin 8 and boss 52 on one hand and the casing 4 on the other.

When the boss 52 and bobbin 8 move downward by the action of the spring20, the bottom bobbin teeth 48 are inserted into the recesses 50 of theplate 9. Then, the casing 4 and the plate 9 slip by approximately2.sub.π /16 radians relative to the bobbin 8. Then, as previouslymentioned, the cords 11 are fed while the bobbin 8 slips relative to thecasing 4. When the bottom bobbin teeth 48 engage the recesses 50 of theplate 9, the bobbin 8 and the boss 52 again rotate together with theplate 9 and the casing 4.

Therefore, the fifth embodiment allows the operator to freely set thelength of the cord 11 by hitting the boss 52 against the ground asdesired.

In another mode shown in FIG. 49, stopper pins 25 are inserted into thebores 22 of the housing 5 and the bores 23 of the plate 9. The stopperpins 25 prevent the cords 11 from being automatically fed and allow onlythe tap-and-go system to operate.

Sixth embodiment

The sixth embodiment of the present invention is described below withreference to FIGS. 50 through 58. Again the differences from the firstembodiment are stressed.

As shown in FIG. 50, a center boss 54 is movably located at the centerof a bobbin 8 and a control plate 9 along an axis 7a. The boss 54 isexposed outside through the center of a cover 6. As shown in FIGS. 50and 53, a plurality of engaging projections 54a protrude from the boss54 and slidably engage the plate 9. The boss 54 can always rotatetogether with the plate 9 due to the projections 54a.

As shown in FIG. 53, eight teeth 55 are formed on the top margin of theinner periphery of the bobbin 8 at equally spaced intervals. As shown inFIG. 54, eight teeth 56 are also formed on the bottom margin of theinner periphery of the bobbin 8 at equally spaced intervals. The topteeth 55 and the bottom teeth 56 are located at the same angularpositions along the periphery.

Eight teeth 57 are formed on the top margin of the outer periphery ofthe boss 54 at equally spaced intervals and eight teeth 58 are formed atthe bottom side of the outer periphery of the boss 54 at equally spacedintervals. The top teeth 57 are displaced from the bottom teeth 58 by2.sub.π /16 radians.

The boss 54 is urged downward by the spring 20 supported by the housing5. The top teeth 57 of the boss 54 are engaged with the top teeth 55 ofthe bobbin 8 by the action of the spring 20. The bottom teeth 56 of thebobbin 8 are separated from the bottom teeth 58 of the boss 54.

As shown in FIGS. 55, 56, and 57, when the boss 54 is moved upwardagainst the action of the spring 20, the top teeth 57 of the boss 54 areseparated from the top teeth 55 of the bobbin 8. The bottom teeth 58 ofthe boss 54 then engage with the bottom teeth 56 of the bobbin 8.

As shown in FIG. 51, when pins 24 are inserted into only bores 22 of thehousing 5, a cutting head 1 has the automatic and tap-and-go functionssimultaneously. When the casing 4 under the state shown in FIGS. 50 and53 rotates, the plate 9 is rotated due to engagement between the linkstud 12a of each link 12 and the inner step 13a of each radial groove13.

Accordingly, the boss 54 rotates together with the plate 9 through theprojections 54a. The bobbin 8 is also rotated together with the boss 54due to engagement between the top teeth 57 of the boss 54 and the topteeth 55 of the bobbin 8. Cords 11 are rotated due to rotation of thecasing 4 and the bobbin 8 to execute mowing.

When the cords 11 are worn off due to mowing, the speed of the casing 4increases and the centrifugal force acting on each link 12 increasessimilarly to the procedure in the first embodiment. Then, the links 12separate from the axis 7a against the action of a compression coilspring 15. The link studs 12a move from the stop position of each radialgroove 13 to the release position.

In this case, rotation of the casing 4 is not transmitted to the plate9, and the boss 54 and the bobbin 8 slip relative to the casing 4. Thisactions feeds, the cords 11.

When the bobbin 8 slips by approximately 2.sub.π /8 radians relative tothe casing 4 and the cords 11 are extended by a corresponding length,the speed of the casing 4 decreases and the centrifugal force acting oneach link 12 decreases. Accordingly, the links 12 moved toward the axis7a by the action of the spring 15 and the link stud 12a move to the stopposition of the adjacent radial groove 13. Then, the plate 9, boss 54and bobbin 8 rotate again together with the casing 4. Thus, the sixthembodiment automatically feeds the cords 11 when the cords 11 wear offby a certain length, similarly to the first embodiment.

The following is the description for use of the tap-and-go system. Whenthe boss 54 under the state shown in FIGS. 50, 53 and 54 is hit againstthe ground, the boss 54 moves upward against the action of the spring20. Then, the bottom teeth 58 of the boss 54 enter the rotational routeof the bottom teeth 56 of the bobbin 8 as shown in FIGS. 55, 56 and 57.

When the plate 9, boss 54 and casing 4 slip by approximately 2.sub.π /16radians relatively to the bobbin 8, the bottom teeth 56 of the bobbin 8engage the bottom teeth 58 of the boss 54. Then, the bobbin 8 rotatesagain together with the casing 4. Thus, the cords 11 are fed while thebobbin 8 slips relatively to the casing 4, similarly to the procedure inthe automatic system.

When the boss 54 is moved downward by the action of the spring 20, thetop teeth 57 of the boss 54 enter the rotational route of the top teeth55 of the bobbin 8. When the plate 9, boss 54 and casing 4 slip byapproximately 2.sub.π /16 radians relatively to the bobbin 8, the cords11 are fed from the casing 4 as above mentioned. When the top teeth 55of the bobbin 8 engage with the top teeth 57 of the boss 54, the bobbin8 rotates again together with the plate 9 and the boss 54. Therefore,the sixth embodiment allows the operator to freely set the length of thecord 11 by hitting the boss 54 against the ground as desired.

In another mode in FIG. 58, when stopper pins 25 are inserted into thebores 22 of the housing 5 and the bores 23 of the plate 9, automaticfeed of the cords 11 is prohibited and only the tap-and-go systemoperates.

Seventh embodiment

The seventh embodiment of the present invention is described below withreference to FIGS. 59 through 66. Again the differences from the firstembodiment are stressed.

As shown in FIGS. 59 and 60, a drive link ring 65 is rotatably providedat the center of a rotary casing 4 about an axis 7a. As shown in FIG.63, a center boss 61 is provided around the shaft of the ring 65. Theboss 61 is spline-fitted with the ring 65. Therefore, the boss 61 canrotate together with the ring 65 and vertically move along the axis 7a.

A bobbin 8 is provided on the outer periphery of the boss 61. Splinegrooves 66 are formed on the inner periphery of the bobbin 8. Splinekeys 61a are formed on the outer periphery of the boss 61. The boss 61can rotate together with the bobbin 8 and vertically move along the axis7a due to engagement between the spline grooves 66 and the keys 61a.

The boss 61 is urged downward by a compression coil spring 20. The boss61 is held in the casing 4 due to engagement between a step 63constituting the spline grooves 66 of the bobbin 8 and the keys 61a ofthe boss 61.

As shown in FIGS. 61 and 62, four guide grooves pairs 65a extending inthe radial direction of the ring 65 are formed on the ring 65. As shownin FIG. 59, a pin 62 protrude radially inward from the ring 65 betweenevery pair of guide grooves 65a. A drive link 12 is slidably placed ineach guide groove pair 65a.

A compression coil spring 15 is positioned between each link 12 and thering 65 around each projection 62. Each spring 15 urges each link 12toward the shaft of the ring 65. Each link 12 placed and each spring 15housed in the ring 65, and the ring 65, boss 61 and bobbin 8 rotatetogether in the casing 4.

As shown in FIGS. 59, 64 and 65, tapered guide surface 61b are formed onthe top end of the boss 61. The surfaces 61b extend up to the top of thekeys 61a. A tapered surface corresponding to the tilt of the surface 61is formed at the end of each link 12. Under the normal state shown inFIG. 59, the end of the boss 61 slightly enters the gap between eachlink 12 and the ring 65 while the end of the surface 61b of the boss 61contacts a part of the surface 64 of each link 12.

As shown in FIGS. 59 and 61, radial grooves 13 and guide grooves 14which are the same as those formed on the plate 9 of the firstembodiment are formed on the inner surface of the housing 5. A link stud12a mounted on the top of each link 12 is inserted into each radialgroove 13 of the housing 5.

When the casing 4 under the state shown in FIGS. 59 and 61 rotates, thebobbin 8 is rotated together with the casing 4 due to engagement betweenthe link studs 12a and the inner steps 13a of the radial grooves 13.Then mowing is executed by cords 11 extended from cord feed slots 10.

When the speed of the casing 4 increases due to wearing of the cords 11,the centrifugal force acting on each link 12 increases similarly to theprocedure in the first embodiment. In this case, each link 12 separatesfrom the axis 7a against the action of the spring 15 as shown in FIGS.64 and 66. Then, the stud 12a of each link 12 moves from the stopposition to the release position of each radial groove 13. The bobbin 8is ready to slip relative to the casing 4.

Thus, similarly to the procedure in the first embodiment, when thebobbin 8 slips relative to the casing 4, the cords 11 are fed out of thecasing 4 by the length corresponding to the difference of rotationalangle between the bobbin 8 and the casing 4.

When the speed of the casing 4 decrease due to feed of the cords 11 andthe centrifugal force acting on each link 12 decreases, each link 12 isreturned to the position shown in FIGS. 59 and 61 by the action of thespring 15. Then, the bobbin 8 rotates again together with the casing 4.Thus, the seventh embodiment makes it possible to automatically feed thecords 11 when the cords 11 are consumed, similarly to the firstembodiment.

The cords 11 can also be fed by hitting the boss 61 against the ground,similarly to the procedure in the first embodiment. That is, duringtapping of the boss 61, the boss 61 moves upward against the action ofthe spring 20. And the top end of the boss 61 deeply enters the gapbetween each link 12 and the shaft of the ring 65 as shown in FIG. 65.

As the boss 61 moves upward, each link 12 is pushed out against theaction of the spring 15 so that it separates from the axis 7a due toengagement between the surface 61 of the boss 61 and the surface 64 ofeach link 12. Thus, engagement between the stud 12a of each link 12 andthe inner step 13a of each radial groove 13 is released. The bobbin 8 isready to slip relatively to the casing 4. Therefore, the cords 11 arefed out of the slot 10, similarly to the procedure in the automaticfeed.

When the state of hitting the boss 61 against the ground is released,the boss 61 is returned to the position shown in FIG. 59 by the actionof the spring 20. As the boss 61 moves downward, the links 12 are pushedback by the action of the springs 20 so that they approach the axis 7a.When the links 12 return to the position shown in FIG. 59, the bobbin 8rotates again together with the casing 4. Thus, the seventh embodimentallows the operator to freely feed the cords 11 by tapping as desired,similarly to the first embodiment.

Eighth embodiment

The eighth embodiment of the present invention is described below withreference to FIGS. 67-72.

As shown in FIGS. 67 and 68, a bobbin 8 is provided in a rotary casing 4consisting of a housing 5 and a protective cover 6. The bobbin 8 canrotate about and vertically slide along an axis 7a of the casing 4.

The bobbin 8 is constructed by connecting an upper flange 75 with alower flange 77 by a cylindrical body (not illustrated). Eight teeth75a-75h are formed on the outer periphery of the upper flange 75 atequally spaced intervals. Similarly, eight teeth 77a-77h are formed onthe outer periphery of the lower flange 77 at equally spaced intervals.The upper flange teeth 75a-75h are displaced from the lower flange teeth77a-77h of the lower flange 77 by the angle of 2.sub.π /16 radiansrespectively.

A center boss 78 is located at the bottom center of the bobbin 8. Acompression coil spring 79 is provided in the cylindrical body of thebobbin 8. The top end of the spring 79 contacts the housing 5 and thebottom end of it contacts the lower flange 77. The spring 79 urges thebobbin 8 and the boss 78 downward, and the bottom end of the boss 78protrudes under the cover 6.

As shown in FIGS. 67 and 68, a swing lever 80 is rotatably supportedbetween the housing 5 and the cover 6 in the casing 4. The lever 80 hasa first arm 81 at the position approximately corresponding to the heightof the upper flange 75 and a second arm 82 at the position slightlylower than the lower flange 77. The arms 81 and 82 have approximatelyequal length and extend in the approximately opposite direction.

Latching legs 81a and 82a are protruded at the end of the first arm 81and that of the second arm 82 respectively so that they are parallelwith the axis 7a and approach each other. As shown in FIG. 67, thelength of the leg 81a of the first arm 81 is slightly shorter than theinterval between the flanges 75 and 77. The bottom end of the leg 81adoes not contact the lower flange 77.

The leg 81a of the first arm 81 is longer and heavier than the leg 82aof the second arm 82, and the moment of inertia of the first arm 81 islarger than that of the second arm 82. Therefore, when centrifugal forceacts on the lever 80 due to rotation of the casing 4, the lever 80 isswung so that the first arm 81 separates from the bobbin 8. A torsioncoil spring 83 is wound on the lever 80. As shown in FIG. 68, thetorsion spring 83 urges the lever 80 so that the leg 81a of the firstarm 81 approaches the bobbin 8.

As shown in FIG. 67, a partition plate 76 is located between the flanges75 and 77 of the bobbin 8. A cord 11 is wound between the upper flange75 and the plate 76 and between the plate 76 and the lower flange 77respectively. As shown in FIG. 68, the upper cord 11 is led to a cordfeed slot 10 via the leg 81a of the first arm 81 and extended to theoutside of the casing 4.

When the cords 11 are extended by a certain length or more out of theslots 10, the end of the first arm 81 engages with the tooth 75a of theupper flange 75 as shown in FIGS. 68. Therefore the bobbin 8 rotatestogether with the casing 4.

The force F1 acts on the lever 80, which swings the lever 80 so that thefirst arm 81 separates from the bobbin 8 due to rotation of the casing4. A tensile force of the cord 11 tends to further extend the cord 11outward on the basis of the centrifugal force due to rotation of thecasing 4 and the resistance produced when the cord 11 collides withgrass. Then, the tensile force acts on the lever 80 as the force F2 forswinging the lever 80 so that the first arm 81 approaches the bobbin 8.

When the extended length of the cord 11 is secured at a certain value ormore, the speed of the casing 4 is kept at the normal speed range (4,000to 6,000 rpm). In this case, the sum of the force F2 caused by thetension of the cord 11 and the urging force F3 of the spring 83 islarger than the force F1 caused by the centrifugal force acting on thelever 80. Therefore, as shown in FIG. 68, the lever 80 is held at theposition where the first arm 81 engages with the tooth 75a of the upperflange 75. As a result, the casing 4 rotates together with the bobbin 8.

Under the above state, the cord 11 is not fed from the bobbin 8. The leg82a of the second arm 82 is placed outside the rotational route of theteeth 77a-77h of the lower flange 77.

When the cord 11 is worn off due to mowing, the speed of the casing 4increases similarly to the procedure in the first embodiment and thecentrifugal force acting on the lever 80 increases. Then, the force F1caused by the centrifugal force acting on the lever 80 gets larger thanthe sum of the force F2 caused by the tension of the cord 11 and theurging force F3 of the spring 83. Accordingly, as shown in FIG. 69, thelever 80 is swung so that the first arm 81 separates from the bobbin 8.According to the swing, the leg 82a of the second arm 82 is brought intothe rotational route of the teeth 77a through 77h of the lower flange77.

When the end of the first arm 81 disengages from the tooth 75a of theupper flange 75, the bobbin 8 slips relative to the casing 4. When thebobbin 8 slips by 2.sub.π /16 radians relative to the casing 4, thetooth 77b of the lower flange 77 engages with the leg 82a of the secondarm 82. The bobbin 8 rotates again together with the casing 4. Accordingto relative rotation between the bobbin 8 and the casing 4, the cords 11are fed outside the casing 4 by the length corresponding to thedifference of rotational angle between the bobbin 8 and the casing 4.

When the speed of the casing 4 decreases because the cord 11 is fedoutward, the centrifugal force acting on the lever 80 decreases and theforce F1 for the lever 80 to push back the cord 11 decreases. Then, thesum of the force F2 caused by the tension of the cord 11 and the urgingforce F3 of the spring 83 gets larger than the force F1. The lever 80returns from the position in FIG. 69 to the position in FIG. 68.

When the leg 82a of the second arm 82 disengages from the tooth 77b ofthe flange 77, the bobbin 8 slips relative to the casing 4 similarly tothe above mentioned embodiments. When the bobbin 8 slips by 2.sub.π /16radians relatively to the casing 4, the end of the first arm 81 engageswith the tooth 75h of the upper flange 75. Thus, the cords 11 are fedoutside the casing 4 by the length corresponding to the difference ofrotational angle between the bobbin 8 and the casing 4. Therefore, asthe cords 11 are worn off, they are automatically fed outside the casing4 by the length corresponding to the angle of 4.sub.π /16 radians.

The following is the description for feed of the cords 11 by thetap-and-go function. When the boss 78 of a cutting head 1 under thestate shown in FIGS. 67 and 68 is hit against the ground, the boss 78and the bobbin 8 move upward against the action of the spring 79 asshown in FIG. 70. Accordingly, the tooth 75a of the upper flange 75disengages from the end of the first arm 81, the bobbin 8 is ready toslip relatively to the casing 4. According to rotation of the casing 4,the bobbin 8 slips by 2.sub.π /16 radians relatively to the casing 4.Then, as shown in FIG. 70, the tooth 77a of the lower flange 77 engageswith the leg 81a of the first arm 81. Thus, the cords 11 are fed outsidethe casing 4 by the length corresponding to the difference of rotationalangle between the bobbin 8 and the casing 4.

When the state of hitting the boss 78 against the ground is released,the boss 78 and the bobbin 8 are moved downward by the action of thespring 79 and return to the state shown in FIG. 67. In this case, thetooth 77a of the lower flange 77 disengages from the leg 81a of thefirst arm 81. Then, similarly to the above mentioned, the bobbin 8 slipsrelatively to the casing 4 until the end of the first arm 81 engageswith the tooth 75h of the upper flange 75. The cords 11 are fed outsidethe casing 4 by the length corresponding to the difference of rotationalangle between the bobbin 8 and the casing 4.

Thus, the head 1 of this embodiment has both the automatic andtap-and-go cord feed functions. For this embodiment, only one lever 80is used in the housing 5. However, it is possible to use a plurality oflevers 80 corresponding to the number of slots 10.

In another mode shown in FIGS. 71 and 72, a bore 84 is formed on thehousing 5 and a stopper pin 85 is inserted into the bore 84. The pin 85has the length from the housing 5 to the first arm 81 of the lever 80.The pin 85 engages with the first arm 81 to inhibit the swing of thelever 80 caused by the centrifugal force. Therefore, insertion of thepin 85 into the bore 84 prevents the cords 11 from being automaticallyfed and allows only the tap-and-go system to operate.

Although eight embodiments of the present invention have been describedherein, it should be apparent to those skilled in the art that thepresent invention may be embodied in many other specific forms withoutdeparting from the spirit or scope of the invention. For example, thepresent invention may be executed in the following modes.

It is possible to arrange the long stopper pins used for some of theabove embodiments so that they can move between the position where theirends stop within the bores of the housing and the position where theirends reach up to the bores of the control plate. In this case, aremote-controller may be combined with the cutting head to control theposition of the pins.

Only one slot 10 or multiple slots 10 may be provided on the cuttinghead 1. Then the number of cords 11 can be changed according to thenumber of slots 10.

Eight radial grooves 13 and guide grooves 14 of the plate 9 are used forsome of the above embodiments. However, the number of those grooves canbe changed in the range of 6 to 12. Also, the number of links 12 can bechanged according to the number of the grooves. Therefore, the presentexamples and embodiments are to be considered as illustrative and notrestrictive and the invention is not to be limited to the details givingherein, but may be modified within the scope of the appended claims.

We claim:
 1. A cutting head for a cord-type mower having a motor fordriving the cutting head, the cutting head being capable of automaticand manual cord feeding, the cutting head comprising:a casing driven bythe motor to rotate about an axis; a bobbin disposed within said casing,and adapted to rotate around said axis relative to said casing, saidbobbin being movable along said axis relative to said casing, between afirst position and a second position; a spring disposed within saidcasing for urging said bobbin toward said first position from saidsecond position, said bobbin being switched from said first position tosaid second position against the action of said spring, in response to atapping operation; a cord having a distal end wound about said bobbin; acord feed slot provided on said casing, for permitting the distal end ofsaid cord to extend outside said casing, to a suitable cutting position;mutual linkage means provided in said bobbin and said casing, forcoupling said bobbin in said first position to said casing, in order tocause them to rotate simultaneously; rotation control means provided insaid bobbin and said casing, for permitting said bobbin, already in saidsecond position, to rotate by a predetermined angle, relative to saidcasing; switching means for automatically switching said bobbin betweensaid first and second positions, in accordance with a rotational speedof said casing, which varies as a function of the length of the cordthat is extended from said cord feed slot, said switching meansincluding:a tapered surface formed on said bobbin, in a radial directionrelative to said axis, said tapered surface forming an aperture at thecenter of said bobbin; a plurality of drive links provided in saidcasing, for reciprocating relative to said axis, along said taperedsurface, each drive link being capable of moving between an operationalposition for pressing said bobbin toward said second position againstthe action of said urging means, and a retracted position for permittingsaid bobbin to remain in said first position, without pressing saidbobbin, each drive link moving to said operational position from saidretracted position, according to centrifugal force of each drive linkdepending on the rotational speed of said casing, thereby causing saidbobbin to be switched to said second position; and bias means for urgingsaid drive links toward said retracted position from said operationalposition, said bias means including a plurality of springs forconnecting adjacent drive links, whereby, when the rotational speed ofsaid casing decreases as a function of the cord feeding, said bias meanscauses said drive links to return to said retracted position from saidoperational position, thereby permitting said bobbin to return to saidfirst position.
 2. The cutting head according to claim 1, wherein saidmutual linkage means includes:a plurality of first engaging portionsformed on said bobbin around said axis; and a plurality of secondengaging portions which are formed on the inner surface of said casingthat faces the outer surface of said bobbin, and which are positionedsuch that they can be engaged with said first engaging portions.
 3. Thecutting head according to claim 1, wherein said rotation control meansincludes:a plurality of first engaging portions formed on said bobbinaround said axis; and a plurality of second engaging portions formed onsaid casing, such that they can be engaged with said first engagingportions when said bobbin is in said second position in response to atapping operation, whereby the engagement of said first and secondengaging portions prevent said bobbin from rotating relative to saidcasing, so as to determine the length of the cord to be extended.
 4. Thecutting head according to claim 1, wherein each of said drive links hasa tapered surface for contacting said tapered surface of said bobbin. 5.The cutting head according to claim 1 further comprising stopper means,said stopper means abutting said drive links to prevent said drive linksfrom moving to said operational position from said retracted position,said stopper means disabling the automatic feeding operation of thecutting head.
 6. The cutting head according to claim 5, wherein saidstopper means includes a plurality of pins fitted to said casing, forengaging each of said drive links.